The desmosomal cadherins are cell-cell adhesion molecules that are essential for epidermal integrity. Of the seven desmosomal cadherins expressed in human epidermis, desmoglein 1 (Dsg1) is a particularly prominent disease target. While the existence of inherited, autoimmune and bacterial toxin-mediated skin disease underscores Dsg1's importance in maintaining adhesion in the suprabasal layers, data from the last funding period demonstrate that Dsg1 also engages signaling mediators to promote terminal differentiation. The objective of this work is to identify how Dsg1 is transported to membranes to correctly perform its adhesion and signaling functions, and to determine how Dsg1-mediated signaling scaffolds promote differentiation. We hypothesize that Dsg1 is physically and functionally coupled to the initiation of the suprabasal differentiation through mitogen activated protein kinase (MAPK) and Rho GTPase signaling switches. We will use imaging, biochemistry and genetic interference in vitro in 2D and 3D organotypic cultures and in vivo in human/mouse xenografts, and complement these studies with analysis of material from patients with Dsg1 mutations, to address the following aims: 1) Determine the mechanism of Dsg1 export from the endoplasmic reticulum and transport to the plasma membrane through plus and minus end-directed microtubule motors in the kinesin and dynein families as well as the Dsg1-associated adaptor complex PX-RICS/14-3-3, 2) Determine how Dsg1 dampens mitogen activated protein kinase (MAPK) signaling through its associated protein Erbin to promote epidermal differentiation, and test the importance of this pathway in striate palmar plantar keratoderma (SPPK), and 3) Determine how Dsg1 and its associated protein Erbin regulate RhoGTPase-dependent signaling to promote actin remodeling, control cell shape and regulate serum response factor (SRF)-mediated transcriptional programs necessary for epidermal differentiation. Elucidating how cytoarchitectural scaffolds choreograph chemical signaling to promote differentiation will be essential for treating skin diseases where these pathways are undermined through cadherin gene defects, autoantibodies or bacterial pathogens. PUBLIC HEALTH RELEVANCE: This project aims to understand how sticky molecules on the surface of skin cells facilitate the formation of cell sheets to provide an essential skin barrier covering the surface of the body. The studies focus on new functions for these molecules, beyond their role in cell coherence, that control normal tissue development and disease processes. These new pathways are predicted to provide novel therapeutic targets for people with inherited, autoimmune and infectious diseases of the skin.